Electrostatic focussing devices especially for microwave tubes

ABSTRACT

The focussing devices of the invention comprise a metal electrode (6) assembled in the envelope (10) through which the electron beam being focussed propagates, said assembly being realised by means of a fixing system comprising a flexible skirt (11) attached around the envelope, and rigid insulating components rigidly attached on the one hand to the electrode (6) and on the other to the skirt (11).

1i 19 [ll] 3 79@,843 Bert et a1. F e10. 1974 [54] ELECTROSTATICFOCUSSING DEVHCES 3,449,617 6/1969 K166611611 et al. 315/534 ESPECIALLYFOR WCRQWAVE TUBES 3,409,794 11/1968 l'leathcote 313/261 3,483,41912/1969 Luebke 315/534 [75] en Alam B9111; Roger Emalhert; P1191792,972,079 2/1961 Wolkstein... 313/256 x Kern, all of Paris, France3,436,588 4/1969 l-lechtel..... SIS/5.34 X 3,681,643 8/1972 Blatter313/261 [73] Asslgnee: Thomson'csm Pans Frame 3,295,000 12 1966 Johnson313/256 [22] Filed: Apr. 5, 1972 Primary Examiner-Rudolph V. Rolinec[211 Appl' 241163 Assistant Examiner-Saxfield Chatmon, Jr.

Attorney, Agent, or Firm-John W. Malley et a1. [30] 11 orelgnApplication Priority Data Apr. 27, 1971 France 71.14989 [57] 52 us. 131315/534, 313/256, 313/287, Th9 focussihg devices of the inventioncomprise 252 metal electrode (6) assembled in the envelope (10) 51 1111.C1. 11011 23/08 through which the electron beam being focussed P [58]Field 61mm... 315/534, 5.35; 313/256, 261, agates, said assembly beingrealised y means of a 313 2 7 253 252 ing system comprising a flexibleskirt (11) attached around the envelope, and rigid insulating components5 References Cited I rigidly attached on the one hand to the electrode(6) UNITED STATES PATENTS and on the other to the skirt (111). 2,825,8353/1958 Heppner 313/153 x 9 means, 7 Drawing Figures PATENTED FEB 5|974SHEET 1 0F 3 PATENTED FEB 5 I974 SHEEI 2 (IF 3 PATENTED FEB 51974 SHEET3 OF 3 ELECTROSTATIC FOCUSSING DEVICES ESPECIALLY FUR MICROWAVE TUBESThe present invention relates to improvements in electrostatic electronbeam focussing devices, or electrostatic lenses. It relates moreparticularly to electrostatic lenses for microwave tubes and to themeans by which they are attached in such tubes.

The problems of focussing electron beams are very important in microwavetubes and more particularly in tubes where the beam passes over a longtrajectory and where important defocussing may arise. This is the case,for example, in multicavity klystron amplifiers where efficientfocussing is essential in the drift spaces between the differentcavities.

Magnetic focussing devices are frequently used, because their userequires less accuracy than do electrostatic focussing devices. Inelectrostatic devicesthe positioning of the focussing device must beextremely accurate and the electrical insulation gives rise to extremelydelicate technological problems. The major drawback of magneticfocussing devices is their weight, which is very much higher than thatof electrostatic focussing devices and becomes prohibitive if the tubesto which they are fitted are part for example of airborne equipment.

Electrostatic focussing devices for microwave tubes generally comprisean annular conductive electrode, of

a toroidal shape for example, raised to a negative po-- tential inrelation to the reference potential which is that of the tube body forexample, thus constituting together with said body an electrostatic lenscentred on the axis of the beam and being attached to the tube enclosureby a fixing system which both maintains the electrode in the properposition and electrically insulates it from the other tube components.

The design of this fixing or attachment system is a particularlydelicate matter. In other words, the position of the electrode must behighly accurate at the time of manufacture of the tube, must remain soduring the various stages of its manufacture, in particular the stovingoperation, and must also remain so during use. Thus, a system which isaccurate from the beginning of its construction is required thedeformations appearing in this system during the stoving operation mustnot modify the centering of the electrode furthermore said system mustbe extremely stable during operation of the tube, and particularly ifthe tube is inserted in an airborne equipment which is subjected tosevere vibrations.

The known fixing or attachment devices make use of several artifices inorder to try to resolve these various problems. For example, the systemfor fixing the electrode to the tube comprises alumina rods which areinserted into the electrode without being soldered or brazed thereto andwhich are assembled onto the tube enclosure or envelope by means ofelements having one degree of freedom, in order to avoid the appearanceof eccentricity during the stoving operation due to the expansion of theelectrode and of the alumina rods in particular such a non-rigid fixingsystem makes it difficult to obtain a convenient centering and possiblyinvolves twisting phenomenous, the electrode axis then making an anglewith the axis of the electron beam. Moreover, it has major drawbacks asfar as achieving good vibration resistance is concerned.

The object ofthe invention is to provide an electrostatic focussingdevice in which the system for attaching the electrode to the envelopeprovides both good electrical insulation and accurate and stablepositioning of the electrode in relation to the electron beam axis, thisboth during manufacturing and during operation of the tube, even insituations where the device is subjected to severe vibrations.

In accordance with the invention, an electrostatic device for focussingan electron beam propagating within an envelope along an axis which. isfixed in relation to said envelope, and comprising an annular electrodehaving applied a potential which is negative in relation to saidenvelope by means of a voltage supply lead penetrating within saidenvelope, and a system for fixing said electrode to said envelope whileassuming that they are electrically insulated from one another, and thatsaid electrode is centered onto the axis of the electron beam, saidsystem comprising a flexible skirt attached to the interior of saidenvelope around the axis of the electron beam, and components made ofrigid insulating material which maintain said electrode rigidly fixed tosaid skirt, said skirt comprising an opening for the passage of saidvoltage supply lead.

Other objects, characteristics and results of the invention will becomeapparent from the ensuing description given by way of non-limitativeexample and illustrated by the attached figures in which FIG. 1illustrates a schematic sectional view of part of a klystron equippedwith an electrostatic focussing device in accordance with the inventionFIG. 2 is a sectional view on X of part of FIG. 1

FIG. 3 is a fragmentary sectional view of part of FIG. 1, in accordancewith a variant embodiment and,

FIGS. 4, 5, 6 and 7 are simplified sectional views equivalent to that ofFIG. 2, illustrating different embodiments of the device in accordancewith the invention.

FIGS. 1 and 2 illustrate an embodiment of a focussing device inaccordance with the invention, applied to a klystron. It goes withoutsaying that this kind of device can be applied to other kinds ofmicrowave tubes and even to other kinds of equipment than such tubes itcan be utilised in any equipment which requires accurate focussing of anelectron beam whose axis is fixed in relation to the envelope orenclosure through which it is propagating.

In FIG. 1, a section through a drift space 1 between two cavities 2 and3, of a klystron, has been illustrated. The axis AB designated both thebeam axis (the beam has not been shown) and the direction of propagationof the beam. The walls constituting the two cavities of the klystron andthe envelope surrounding the drift space 1, are made of metal and are ata reference potential which is for example the earth potential. Thepassage of the electron beam along the axis AB, between cavities anddrift space, takes place through the openings d and 5.

FIG. 2 schematically illustrates a view of this drift space l as itappears after making section along X (FIG. 1) and removing all the partto the left of X.

A consideration of these two figures where similar references correspondto similar elements, will show how an embodiment of the focussing devicein accordance with the invention is arranged.

An electrostatic lens is constituted in a manner known per se, by ametal annular electrode 6 cooperatv 3 ing with the body of the tube andforming a solid of revolution therewith. Said electrode, for example oftoroidal form, is centered on the axis AB by a fixing system formingpart of the invention, and is brought to a negative potential inrelation to the reference potential hereinbefore referred to, by voltagesupply means 9 described hereinafter.

The system for fixing the electrode 6 to the cylindrical envelope 10comprises a flexible skirt 11 of cyclindrical form, constituted forexample by a thin copper sheet profiled in the manner indicated by itssection 12 (FIG. 1) and brazed by its edges to the interior of the metalenvelope 10 in which the focussing electrode 6 is arranged. Said skirt11 is opened over part 13 of its periphery in order to pass the voltagesupply lead 9; this opening, of course, corresponds with the voltagesupply connection 14 assembled on the body of the tube. It should benoted that the profile of the section 12 of the skirt 11 can differ fromthat shown in FIG. 2 in all cases, it must be such that the skirt hasadequate flexibility. FIG. 3 illustrates a variant embodiment of thisprofile, which is simple to create.

The system of fixing the electrode 6 comprises, furthermore, two rods 15and 16 which are cylindrical in the embodiment shown in FIGS. 1 and 2.These rods are attached to the electrode 6 at two diametrally oppositepoints by two components 7 and 8 which are integral with the electrodeand each provided with a hole whose axis is perpendicular to the axisAB. The axes of said holes are substantially parallel with one anotherand the two rods 15 and 16 each passes through one of said holes in therespective components 7 and 8. These two rods are constituted by arigidmaterial which is a good electrical insulator, for example alumina, andare rigidly attached to the components 7 and8 by brazing for example.

The points of attachment of the rods 15 and 16 to the skirt I1 and thelength of these rods are chosen so that the axis of the electrode 6coincides accurately with the axis AB of the envelope'10 forming thedrift space 1. In the example described, where the two rods 15 and 16are equidistant from the axis of the electrode 6, the rods have the samelength.

The voltage supply lead 9, which can be applied at any point on theelectrode 6, will here advantageously be connected to one of the twocomponents supporting the rods, for example the component 7 which isthen made up of conductive material which may be the same as thatconstituting the electrode 6, e.g. stainless steel. In some manufactureembodiments, the components 7 and 8 can form part of the electrodeitself in others, they are attached thereto and soldered or brazed inposition.

As FIG. 1 indicates, the voltage is applied to the electrode 6 through ametal wire 17 located in a metal tube 18, the wire being brazed orsoldered to the component 7 at one of its ends and to the metal tube 18at its other end. The tube '18 is inserted with one end in the component7 whose top part is provided with a recess 19 for this purpose its otherend is connected to an insulating pot 20 which surrounds it in order toprovide good insulation of the negative voltage supplied to theelectrode 6, which voltage may be very high in relation to the referencevoltage of the body of the klystron. The diameter of the metal tube 18is chosen so as to minimise the electric field produced in the envelope10 between said tube and the body of the kylstro'n.

A connection 14 which has not been described here in a detailed way, butwhich can be of any known kind, is used to attach the pot 20 to theklystron body.

As already mentioned, the tube 18 constituting the voltage supply lead 9passes through the open part 13 of the skirt 11.

An electrostatic focussing device such as that described, has severalimportant advantages.

One advantage is that all the components constituting the system used toattach the electrodes 6 to the envelope 10, are connected together bysoldering or brazing. The risk in the variation of the relativepositions, is thus virtually eliminated, even in the presence ofvibration. As already pointed out, these rigid connections run no riskof effecting the centering of the electrode even during the stoving ofthe tube. In other words, the flexibility of the skirting 11 enables itto absorb the distortions and differential expansions of thesecomponents, for example the electrode 6 and the rods 15 and 16. If thecentering of the electrode 6 on the axis AB of the klystron isaccurately established at the time of assembly, then it will remain soduring the various phases of manufacture of the tube and duringoperation thereof thanks to the flexibility of the skirt 11, thiscentering will be maintained oven if the tube is used in airborneequipment subjected to vibration.

However, the accuracy of the centering at the time of assembly is quitean easy matter to arrange. In other words, the electrode 6, the rods 15and 16 and the skirt 11 constitute a sub-assembly which can bemechanically set prior to assembly in the envelope 10, and thensubsequently brazed or soldered in position in said envelope. At thismoment, the centering of the electrode 6 on the axis AB can be effectedsimply and accurately with the help of a gauge block for examle whichcooperates with the envelope l0 and the internal diameter of theelectrode 6.

Another advantage of this device is that the components which make upthe fixing system, are simple and consequently inexpensive.

It should be noted that this kind of focussing device and its voltagesupply system have much higher resonance frequencies than the prior artones which are generally heavier. This makes them particularly relevantto application in airborne equipment.

FIGS. 4, 5, 6 and 7 illustrate in a highly schematic manner equivalentviews to that of FIG. 2 (section on X in FIG. 1) of other embodiments ofthe device in accordance with the invention. In these figures,references identical to those of H02, indicate identical elements.

In the embodiment of FIG. 4, the cylindrical rods 15 and 16 arereplaced'bygrooved rods 31, 32 in order to increase the distanceobtained between the electrode 6 and the skirt 11 over the surface ofthe rods 31 and 32, thus lengthening the pass of the leakage currentsand improving the breakdown voltage conditions. In this case, thecomponents 7 and 8 no longer contain a cylindrical hole but are slottedas in the preceding cases, the rods are soldered or brazed to thesecomponents.

In FIGS. 5 and 6, cylindrical rods 15 and 16 of FIG. 2 have beenreplaced by flat components 40 and 50 of rigid insulating material suchas alumina, soldered or brazed to the skirt 11 and directly attached,likewise by soldering or brazing, to the electrode 6. The shape of thesecomponents is such that the distance between the electrode and the skirtover their surface, is as long as possible in order to improve thevoltage breakdown stability. In'these two examples, the voltage supplylead 9 again takes the form, as before, of a wire inside a metal tube,the tube being inserted into a metal component, respectively 41 and 511,part of which, respectively 42 and 52, is attached by soldering orbrazing, to the electrode 6.

In the embodiment shown in FIG. 7, the technology used to manufacturethe electrode 6 is different. This time, an insulating plate 60 ofalumina for example, is machined centrally in accordance with thetoroidal form of the electrode, the electrode being constituted by aconductive deposit 63, metallic for example, having a thickness of somefew tenths of a millimeter, applied to the toroidal zone. The voltagecan be supplied at 9, as before, to a metal component 61 attached to theplate 60 and electrically connected to the deposit 63 which constitutesthe electrode, by a metallized zone 62 for example. The plate 60 ismachined in order to increase the length of the path of the leakagecurrents it is for example pierced by slots such as those 64.

What I claim is:

1. An electrostatic device for focussing an electron beam propagatingwithin an envelope along an axis which is fixed in relation to saidenvelope which constitutes a surface of revolution around the axis ofsaid beam, comprising:

an annular electrode having applied thereto a potential which isnegative in relation to said envelope by means of a voltage supply leadpenetrating within said envelope; and

a system for fixing said electrode to said envelope in an electricallyinsulated relationship from one another, said electrode being centeredwith respect to the axis of the electron beam, said system comprismg:

a flexible cylindrical skirt attached to the interior of said envelopearound the axis of the electron beam, said skirt exhibiting a profiledsection in planes containing said axis, the edges of said skirt beingattached to said envelope whereby the skirt is elastically deformablebetween its edges; and

components of rigid insulating material attached on the one hand to thesaid electrode, and on the other hand to said skirt between the said twoedges, said skirt further having an opening therein for the passage ofsaid voltage supply lead.

2. A focussing device according to claim 1, wherein said components madeof rigid insulating material are constituted by two cylindrical rodshaving the same length, fixed at their mid-points to the electrode bymeans of two pieces which are themselves attached onto two diametricallyopposite points of said electrode, said two pieces being each providedwith a hole whose axis is perpendicular to the axis of said electrode,the two rods passing respectively through said two holes where they arerigidly fixed to the said two pieces in order to be parallel with oneanother and symmetrical in relation to the axis of the electrode andbeing furthermore rigidly attached by their ends to said skirt.

3. A focussing device according to claim 2, wherein at least one of thetwo said pieces in which the two cylindrical rods are fixed, is ofaconductive material, located in front of said opening of said skirt, andconnected to said voltage supply lead.

a. A focussing device according to claim 2 wherein said two rods ofrigid insulating material are grooved, the two holes in which they areinserted and fixed into the said two pieces which are attached to theelectrode, being open over part of their peripheries.

5. A focussing device according to claim 1 wherein said components ofrigid insulating material are constituted by a fiat plate disposedperpendicularly to the axis of said electrode and attached rigidly onthe one hand to said skirt and on the other to said electrode which saidskirt maintains centered onto the axis of said electron beam.

6. A focussing device according to claim 5 wherein said flat plate iscut out in order to increase the path for the leakage currents betweensaid electrode and said skirt.

7. A focussing device according to claim 1, wherein said components ofrigid insulating material comprise a flat plate arranged perpendicularlyto the axis of the electron beam and rigidly attached to said skirt,said electrode including a film of conductive material de posited onto atoroidal zone machined at the center of said flat plate.

8. A microwave tube having an electrostatic device for focussing anelectron beam propagating within an envelope of said tube along an axiswhich is fixed in relation to said envelope which constitutes a surfaceof revoluation around the axis of said beam, comprising:

an annular electrode having applied thereto a potential which isnegative in relation to said envelope by means of a voltage supply leadpenetrating within said envelope; and

a system for fixing said electrode to said envelope in an electricallyinsulated relationship from one another, said electrode being centeredwith respect to the axis of the electron beam, said system comprismg:

a flexible cylindrical skirt attached to the interior of said envelopearound the axis of the electron beam, said skirt exhibiting a profiledsection in planes containing said axis, the edges of said skirt beingattached to said envelope whereby the skirt is elastically deformablebetween its edges; and

components of rigid insulating material attached on the one hand to saidelectrode, and on the other hand to said skirt between the said twoedges, said skirt further having an opening therein for the passage ofsaid voltage supply lead.

9. A microwave tube according to claim 8, wherein said tube is amulticavity klystron having a drift space separating the cavities ofsaid klystron, the focussing device being positioned in said driftspace.

* :k t= =l =i=

1. An electrostatic device for focussing an electron beam propagatingwithin an envelope along an axis which is fixed in relation to saidenvelope which constitutes a surface of revolution around the axis ofsaid beam, comprising: an annular electrode having applied thereto apotential which is negative in relation to said envelope by means of avoltage supply lead penetrating within said envelope; and a system forfixing said electrode to said envelope in an electrically insulatedrelationship from one another, said electrode being centered withrespect to the axis of the electron beam, said system comprising: aflexible cylindrical skirt attached to the interior of said envelopearound the axis of the electron beam, said skirt exhibiting a profiledsection in planes containing said axis, the edges of said skirt beingattached to said envelope whereby the skirt is elastically deformablebetween its edges; and components of rigid insulating material attachedon the one hand to the said electrode, and on the other hand to saidskirt between the said two edges, said skirt further having an openingtherein for the passage of said voltage supply lead.
 2. A focussingdevice according to claim 1, wherein said components made of rigidinsulating material are constituted by two cylindrical rods having thesame length, fixed at their mid-points to the electrode by means of twopieces which are themselves attached onto two diametrically oppositepoints of said electrode, said two pieces being each provided with ahole whose axis is perpendicular to the axis of said electrode, the tworods passing respectively through said two holes where they are rigidlyfixed to the said two pieces in order to be parallel with one anotherand symmetrical in relation to the axis of the electrode and beingfurthermore rigidly attached by their ends to said skirt.
 3. A focussingdevice according to claim 2, wherein at least one of the two said piecesin which the two cylindrical rods are fixed, is of a conductivematerial, located in front of said opening of said skirt, and connectedto said voltage supply lead.
 4. A focussing device according to claim 2wherein said two rods of rigid insulating material are grooved, the twoholes in which they are inserted and fixed into the said two pieceswhich are attached to the electrode, being open over part of theirperipheries.
 5. A focussing device according to claim 1 wherein saidcomponents of rigid insulating material are constituted by a flat platedisposed perpendicularly to the axis of said electrode and attachedrigidly on the one hand to said skirt and on the other to said electrodewhich said skirt maintains centered onto the axis of said electron beam.6. A focussing device according to claim 5 wherein said flat plate iscut out in order to increase the path for the leakage currents betweensaid electrode and said skirt.
 7. A focussing device according to claim1, wherein said components of rigid insulating material comprise a flatplate arranged perpendicularly to the axis of the electron beam andrigidly attached to said skirt, said electrode including a film ofconductive material deposited onto a toroidal zone machined at thecenter of said flat plate.
 8. A microwave tube having an electrostaticdevice for focussing an electron beam propagating within an envelope ofsaid tube along an axis which is fixed in relation to said envelopewhich constitutes a surface of revoluation around the axis of said beam,comprising: an annular electrode having applied thereto a potentialwhich is negative in relation to said envelope by means of a voltagesupply lead penetrating within said envelope; and a system for fixingsaid electrode to said envelope in an electrically insulatedrelationship from one another, said electrode being centered withrespect to the axis of the electron beam, Said system comprising: aflexible cylindrical skirt attached to the interior of said envelopearound the axis of the electron beam, said skirt exhibiting a profiledsection in planes containing said axis, the edges of said skirt beingattached to said envelope whereby the skirt is elastically deformablebetween its edges; and components of rigid insulating material attachedon the one hand to said electrode, and on the other hand to said skirtbetween the said two edges, said skirt further having an opening thereinfor the passage of said voltage supply lead.
 9. A microwave tubeaccording to claim 8, wherein said tube is a multicavity klystron havinga drift space separating the cavities of said klystron, the focussingdevice being positioned in said drift space.